I need ideas for a domain expansion

I have a bubble technique, but it lacks domain expansion (it wasn't missing before, but I ended up not liking my own idea anymore and giving up on the expansion I created), How could I create one that is not too strong but also not too weak? My OC is a very hard working man who tries his best even though his technique is something as simple as creating bubbles. The bubbles cannot be manipulated in any absurd way, the most the user can do is harden them (and with that create tricks like using them as gloves, use as a shield or throwing them to work like bullets), make someone slip or increase the pH of a few bubbles to make them acidic.